Public-Access Defibrillation in Sudden Cardiac Arrest (Short Review)

При внезапной остановке сердца, вызванной фибрилляцией желудочков и желудочковой тахикардией, одним из ключевых способов увеличения успеха догоспитальной и госпитальной реанимации и выживаемости оживленных больных является общедоступная дефибрилляция. В кратком обзоре литературы рассмотрели связь между видом внезапной остановки сердца и выживаемостью, концепцию цепочки выживания и роль ранней дефибрилляции, функции программ по общедоступной дефибрилляции и роль автоматических наружных дефибрилляторов при проведении догоспитальной и госпитальной реанимации. В заключении обсудили перспективу внедрения общедоступной дефибрилляции в России.


Introduction
Sudden cardiac arrest (SCA) caused by cardiac and extracardiac pathology is one of the leading causes of death in developed countries [1]. Mechanisms of SCA development are as follows: a) ventricular fibrillation (VF) and pulseless ventricular tachycardia (PVT), b) asystole (As) and c) electromechanical dissociation (EMD) or the pulseless electrical activity.
Pre-hospital cardiac arrest. In the United States, pre-hospital SCA develops approximately in 350.000 people per year. In Russia, 200.000-250.000 patients suddenly die from heart diseases every year. In most European countries, an average of approximately 87 cases of the SCA per 100.000 people were registered every year before 2010; 84 cases were registered from 2011 to 2015 [2,3].
Over the past 25 years, a progressive decrease in the incidence of VF was observed, which to a certain extent is related to the primary and secondary prevention of heart diseases and the SCA. At that, the time of registration of the arrhythmia is crucial. For example, in the case of a long (> 5-8 min) prehospital cardiac arrest, primary VF before the resuscitation was registered in 25 (20-40)% of patients. However, if ECG could be registered within the first minutes of the SCA at public places equipped with an automated external defibrillator (AED), the primary FV was 49-76% [4,5]. Data of the analysis of the cardiac rhythm carried out from 2006 to 2012 demonstrated that 25-50% of SCA resulted from FV and PVT [1,6,7]. According to two multicenter studies carried out in the United States and Europe from 2011 to 2015, VF and PVT were registered in 15.5 and 12.5-22%, respectively [3,8].
The survival rate of resuscitated patients with pre-hospital FV/PVT in various regions of Canada and the United States before 2010 ranged from 7.7 to 40% (median 22%), while the overall survival after all kinds of pre-hospital SCA (As, EMD, and FV/PVT) ranged only from 3 to 12.6% (median 8.4%) [9]. In European studies, it was found that the survival rate in Denmark increased with the development FV/PVT from 16.3 to 35.7% and As/EMD from 0.6% to 1.8% over the period from 2005 to 2012 [10]. In the Netherlands, over the specified time period, the survival rate increased only in the development of FV/PVT (from 29 to 41.4%); in the case of the development of As/EMD, it almost has not changed (3.1-2.7%) [6]. According to recent studies (2011)(2012)(2013)(2014)(2015), in five US states the survival rate after all kinds of SCA (n=65,000) averaged 11.4% (the range by states varied from 8.0 to 16.1%) and after development of FV/PVT it was 34% (varied depending on the state from 26.4 to 44.7%). In 27 European countries (2014), the survival rate after all kinds of SCA (n=10.600) amounted to 10.7% (by countries: from <5 to 31%), after the primary FV it was 29.7% (by countries: from 5.3 to 58%) and after all the cases of primary and secondary it was on average 21% [3.8].
In-hospital cardiac arrest. According to two studies (1999)(2000)(2001)(2002)(2003)(2004)(2005) in hospitals in the United States and several European countries, the primary FV/PVT was registered in 24-35% of patients; the survival rate in study [12] was an average of 37% and study [13] it ranged from 18 to 67%. In study [14], it was found that in the United States the incidence of the in-hospital VF/PVT decreased from 23.5 to 18.5% over the period from 2000 to 2009; while the survival rate increased from 28 to 39%. When the primary As and EMD develops (about 70% of all SCA cases) the survival rate was on average 11 and 12%, respectively (ranged from 1.2 to 14%) [12,13]. It was also found that during cardiopulmonary resuscitation (CPR) in approximately 20% of patients with the primary asystole or EMD, secondary (i.e. terminal) FV/PVT develops; this combination was associated with a reduced survival rate. For instance, in the case of the primary As with the development of the secondary FV/PVT during the CPR, it was 8% (without secondary FV/PVT it was 12%), and with the primary EMD it was 7% (without secondary FV/PVT it was 14%) [12]. In studies conducted in Norway from 2009 to 2013, the in-hospital primary FV/PVT was registered in 27-32% of patients, As was found in 19-23% and EMD in 48% of patients. The survival rate of patients with FV/PVT amounted to 53% and in patients with a cardiac pathology it was 61%; the survival rate in the case of As was 17%, in the case of EMD it was 13% and the overall survival was 25% [15,16]. In the UK, from 2011 to 2013, in 144 hospitals, the FV/PVT caused SCA in 17% of patients, As in 23.6% of patients, and EMD in 49% of patients; the survival rate was: 49% for FV/PVT, 8.7% for As, and 11.4% for EMD, and the overall survival was18.4% [17]. In Italy, from 2012 to 2014, in 36 hospitals, VF/PVT was registered in 19% of patients; the overall survival was 14.8% [18].
Therefore, both pre-hospital and in-hospital SCA caused by the primary VF/PVT, unlike the SCA caused by the primary As and EMD, is characterized by a significantly higher survival rate of resuscitated patients.
Концепция «цепочки выживания». В начале 90-х годов прошлого столетия экспертами Американской Ассоциации Сердца была сформулирована концепция «цепочки выживания». Согласно этой концепции увеличить успех реанимации и выживаемость больных, перенесших догоспитальную ВОС, можно, если удается: • быстро распознать ВОС и быстро вызвать службу экстренной помощи were placed in airports, airplanes and casinos. This high survival rate after successful resuscitation was provided by the introduction of the «chain of survival» concept and the program of immediate commencement of basic CPR and rapid application of the AED. It should be noted that in cases of development of FV or PVT, every minute of delay of the CPR commencement reduces the probability of the survival by 7-10% and delay of the defibrillation by 10-15%. Unfortunately, even in the leading European countries, a rapid commencement of the resuscitation by an accidental witness of the SCA was undertaken only in a third of cases, and the basic CPR at a high level with the use of the AED was carried out even more rarely. In this regard, the main objective of the 2005 international recommendations on the CPR, as well as changes in educational materials, was to increase the survival rate due to earlier and high-quality basic resuscitation with an extensive use of the AEDs [4,[19][20][21].
It should be noted that the causes of low survival rates after pre-hospital SCA are more difficult to study, especially taking into account requirements of the evidence-based medicine. The lack of a uniform tactics and strategy for resuscitation and its outcomes make the evaluation of study findings of patients of all categories and all emergency services more difficult. Therefore, many studies have focused on short-term and early results of the resuscitation, namely: restoration of spontaneous circulation (actually the success of resuscitation) and the number of patients surviving till hospitalization (short-term survival). However, the main criterion for a successful pre-hospital resuscitation include its delayed and long-term results, namely, the survival of resuscitated patients with the lack of serious neurological disorders at the time of discharge from hospital (delayed survival rates) and survival and quality of life within 1-5 years after resuscitation (long-term survival).
The «chain of survival» concept. The «chain of survival» concept was formulated by experts from the American Heart Association in early 1990s. According to this concept, the success of resuscitation and the survival rate of patients with pre-hospital SCA may be increased, if the following criteria are met: • rapid diagnosis of SCA and quick call to the emergency service; • quick commencement of the CPR by surrounding people. In this case, the survival rate can be increased by more than two-fold [22,23].
• quick defibrillation; • quick access to an expanded CPR and adequate post-resuscitation therapy after successful resuscitation.
A delay in any step leads to a deterioration of the resuscitation results and reduction of the survival rates.
Public-access defibrillation concept. A wide use of the AED outside the hospital by minimally trained personnel without medical education formed the basis of the concept of publicly accessible defibrillation, which was formulated by the American Heart Association experts in 1994. Based on this concept, programs of the pre-hospital use of the AED by the first SCA witnesses were developed in the United States and Europe. According to studies published in 2010-2016, the use the AED by the first SCA witness caused by the primary FV/PVT significantly increases the number of survivors with a satisfactory neurological status [6,[24][25][26][27]. Therefore, a wide use of AEDs can improve outcomes in the case of pre-hospital SCA. However, AED is not frequently used in a number of European countries. For example, according to M. Agerskov et al. [25], in Denmark, the first witnesses of SCA applied the AED before arrival of the EMS for resuscitation of only 3.8% of patients.
Public-access defibrillation (PAD) programs. PAD programs solved a number of tasks, among which the following ones could be named: • contact with a local emergency medicine service or other emergency services • location of the AED and criteria for its selection • principles and quality of training in basic CPR using the AED Contact with a local emergency medicine service and its dispatcher. The European Resuscitation Council Guidelines for Resuscitation 2015 (ERC Guidelines 2015) emphasize the essential role of interactions between an EMS dispatcher and people carrying out the basic CPR. The service dispatcher plays an important role in the early diagnosis of cardiac arrest and carrying out of a high-quality CPR (the so-called telephone CPR monitoring ), as well as in searching for the AED and ensuring its delivery to the scene [1, 28]. Organization of cardiac arrest centers and their contacts with regional and local emergency medical services should be encouraged, because it is associated with an increase in the survival rate and improvement of neurological outcomes in patients with pre-hospital cardiac arrest [1].
Location of the AED and criteria for its selection. There are several criteria for selection of the AED location. The time factor is one of such criteria. It is economically feasible to place the AEDs in those public places where one cardiac arrest may be expected once per 5 years [1,29]. According to ECR experts, the ideal location for the AED must be at such a distance that a person rendering the first aid could spend no more than 1.5 min to fetch it and return to the patient. In this case, an emergency medical care dispatcher can help. For this ной службы играет важную роль в ранней диагностике остановки сердца и выполнении качественной СЛР (т. н. телефонный контроль СЛР), а также поиске и обеспечении доставки АНД к месту происшествия [1,28]. Следует поощрять организацию центров остановки сердца и их контакт с региональными и местными службами экстренной медицинской помощи, так как это сопровождается увеличением выживаемости и улучшением неврологических исходов у пострадавших при догоспитальной остановке сердца [1].
Training in basic CPR using the AED. It should be noted that in the case of the pre-hospital cardiac arrest caused by FV early high-quality chest compression (CC) and defibrillation are key factors to the success of the resuscitation and survival. According to [30,31] effective training of non-professionals in the basic CPR using the AED increases the delayed and longterm survival (by the 30 day and 1 year of observation, respectively). It was also shown that welltrained EMS managers were able to improve resuscitation carried out by people surrounding the patient and its outcomes [1,32].
Public-access defibrillation at hospitals. In the world practice, depending on the model of the device, the AEDs are used in 3 modes at hospitals: semi-automatic, fully automatic and manual. Semi-automatic and, less frequently, manual modes are used in PAD. It should be noted that there are still no results from randomized clinical trials comparing the use of the hospital manual defibrillators and the AED in semi-automatic mode. At the same time, 3 observational studies were conducted which had not found increased survival rates using the AED [33-35] and one study even demonstrated its decrease as compared with the use of manual defibrillators [36]. The results of study [37] suggests that the AED may cause delay in the commencement of the CPR and increase the duration of breaks in the CC associated with the automatic analysis of the rhythm and commands that AED produces during the resuscitation of patients with primary asystole and primary EMD (it is known, that defibrillation is not applied to eliminate the latter). Based on the results, the ERC experts (2015) recommend to use the AED in the semi-automatic mode in those hospitals units where there is a risk of delay in defibrillation for a few minutes (more than 2-3 min) and the first people who have witnessed the SCA have no experience in manual defibrillation. In those hospital units where quick access to defibrillators may be provided, manual defibrillation conducted either by trained personnel or the resuscitation team should be preferred to the use of the AED because it reduces the time from the onset of the SCA to the first discharge. However, in such cases, experience in the visual analysis of the electrocardiogram (ECG) is required [1]. The ERC Guidelines 2015 recommendations for the use of automatic and manual defibrillators for the PAD are based on studies conducted in the United States and Australia [33][34][35][36][37]. It should be noted that no similar studies were conducted in Russia, therefore, at present time, this recommendation can be introduced in the practice of those Russian hospitals which have special resuscitation teams and/or trained staff experienced in a fast analysis of ECG and work with manual defibrillators.

Perspectives of introducing public access defibrillation in Russia.
A complex solution of sociodemographic, epidemiological, medical, technical, legal, economic and organizational issues is required for the wide introduction of high-quality PAD programs. Taking into account the great experience, as well as the complexity of implementation of PAD programs in countries of Western Europe and the United States [11], the solution to this problem in Russia should be implemented step-by-step. The first step is to introduce the PAD in the everyday practice of multidiscipline hospitals (for example, in Moscow and St. Petersburg) with a thorough analysis of the impact of the PAD programs on survival of both individual patients and large patient groups depending on the type of the SCA (FV/PVT, asystole and EMD), diagnosis and the AED mode (semi-automatic and manual). In the future, the obtained results will be used to optimize both the in-hospital and pre-hospital PAD programs (stage 2). Among the latter, PAD programs for the police and fire-fighting services [38], as well as the «home defibrillation» should be noted. Municipal centers of cardiac arrest should be organized to increase the survival rate. According to [39,40], the delayed and longterm survival rate of patients resuscitated before admission to the hospital increased with a high frequency of their admission to specialized centers (more than 100 per year).

Conclusion
In conclusion, the main problems whose solution can improve the success of CPR and survival of patients after cardiac arrest both in public places and in healthcare institutions should be emphasized once again: first, the causes of low survival rates after prehospital SCA are more difficult to study, especially taking into account requirements of the evidencebased medicine; second, the heterogeneity of the population (age, sex, nature of the disease, etc.), as well as the heterogeneity of the resuscitation tactics make the assessment of its results and assessment of the effectiveness of the emergency medical services difficult; third, to improve the SCA treatment, the adoption of high-quality PAD programs and effective functioning of the chain of survival are required. The health system, including the Ministry of Health of the Russian Federation, must monitor the process to ensure a higher level of survival.